This project employs the methods of behavioral neurophysiology to study the frontal lobe of primates. The primate frontal lobe consists of three main parts: the primary motor cortex (Ml), the nonprimary motor cortex, and the prefrontal cortex (PF). The nonprimary motor cortex can be divided into at least two fields: the supplementary motor cortex (M2) and the premotor cortex (PM). It is likely that PM can be further subdivided into a dorsal (PMd) and a ventral (PMv) field. Our results support the hypothesis that, among their functions, PM and M2 play a role in motor preparation. We now believe that PM functions in retrieving from memory the movement that needs to be made on the basis of a sensory event. Consistent with that view is the finding that PM activity guides more than merely the attainment of the target or goal of the movement; the precise details a response is reflected in PM activity. Our first examination of PF activity revealed that the physiological distinctions reported by others are valid reflections of different patterns of physiological organization in PF vs. PM, rather than simply being caused by differences among individual, species or methodological approaches, as some investigators have argued. Electroanatomical and cytoarchitectonic techniques have enabled an improved identification of individual cortical fields and a better understanding of the overall organization of the frontal lobe.